Elucidating the thermometabolism of Thalattosuchus superciliosus (de Blainville) Young, Brignon, Sachs, Hornung, Foffa, Kitson, Johnson & Steel, 2021 (Archosauria: Metriorhynchidae): a paleohistological study

Metriorhynchidae Fitzinger, 1843 is an emblematic group of crocodylomorphs whose marine and pelagic lifestyle has long aroused the interest of palaeontologists. Indeed, both their ecology and thermometabolic strategy (i.e., endotherm or ectotherm) remained debated. In order to shed light on this matter, we inferred the thermometabolism of Thalattosuchus superciliosus de Blainville, 1852 focusing on the femoral histology and CT-scan anatomy. Using “phylogenetic logistic regression” methods, we calculated the probability of endothermy on the basis of minimum vascular cavity diameter. Using the “phylogenetic eigenvector maps” approach, we inferred resting (based on osteocyte density) and maximum (based on minimum diameter of femoral nutrient foramina) metabolic rates. We found that T. superciliosus had a low probability of being endotherm and possessed a low resting metabolic rate. The study of the maximal metabolic rate allows us to suggest that T. supercilious was not a pursuit hunter, but perhaps rather had a sit-and-wait/opportunistic and scavenging feeding strategy, as extant crocodylians. Our study allows us to discuss the ecology of this species, but further studies relying on a wider sample of metriorhynchids are needed in order to have a better understanding of both the thermometabolism and the foraging behavior of this group.